Meaning: The meaning of today's Good Word is, forsooth, none but "truth" and "reality".

Notes: When I was in high school, the North Carolina legislature quite wisely mandated the teaching of one Shakespearean play each year for all four years of high school. I ran with a crowd that not only refused to bemoan this requirement, but read several additional Shakespearean plays each spring. The result was that we became so proficient in the poetical English of the Bard, that we actually conversed in it up and down the halls, much to the bemusement of our schoolmates.

In Play: The upshot was that I collected a catalog of words that should not have been allowed to escape our palates; today's Good Word is one such. It actually still lurks inside other words, like forsooth "truly" and soothsayer "prognosticator, fortune-teller". But why do we no longer hear, "Forsooth, the weather soothsayer predicts mild weather for the weekend. Prithee, should we venture forth to the countryside then?" I think my high school mates and I might have liked these words because they are all purely English and not borrowed from a Romance language.

Word History: The [s] in today's word is actually the same as the [s] in is, for sooth is based on PIE *es- "to be". The present participle of this word was *sont- "being, existing, real, true". That final [t] would have become [th] in Germanic languages. English retained the [th] but lost the [n]; Danish sand "true" and Swedish sann "true" retain the [n] but not the [th]. Other words from *es- include Sanskrit swastika "good luck charm", from su "good" + es-ti "is", forming svasti "well-being", the root of swastika. In the West it has brought no one good luck.

I'm not sure I've ever heard/seen sooth without the for.
As to the shakespearian speech I always likd it but it is very obfuscatory for those not in the loop, were you then using it as a geek secret code? I say geek as it is an intellectual thing, not sports or jock talk.

The obvious word to compare is soothe. Yes, it seems to be the same *es- root.

I'm generally very sceptical when it comes to analyzing one-letter proposed roots and their developments, or efforts to relate words in other languages to Chinese, but I do believe this one. For example, for sōth in OE 'true', Gmc *santhaz, I believe, despite having no children of my own, that it is true parental happiness when you have soothed them enough to make them sleep.